Microscopes use various types of illumination sources to provide the necessary light to illuminate the specimen being examined. Conventionally, these sources consume electrical energy, and the life of the sources is related to the amount of time the sources are active. Leaving a source on too long can also damage the specimen under study. It is desirable then, to conserve operating expense, extend illumination source life, and prevent damage to specimens, to activate the light sources only when the microscope is in use, and de-activate the source when not in use. In normal operation, a microscope user manually activates the illumination source to commence use of the microscope, and may even alter illumination source modes (reflected light, transmitted light or a combination of both modes) during use. Unfortunately, a user may forget to deactivate the light source after use of the microscope, which causes increased operating expense and shortened source life. The problem to be solved, then, is not that of turning on a source of illumination, for this must necessarily be done prior to use, but that of turning off the source after use, for this is not necessary and may be neglected.
Unlike many household and other appliances and electronic equipment that feature “power-down” capability, it is typically desired with microscopes that the “power-down” feature be activated a relatively long time (i.e., as much as an hour or two) after some triggering event. Thus, while it might be desirable to de-energize a household iron a few minutes after non-use, such is not typically the case with a microscope. This is important to note since analog shut-down devices that are sometimes used in such appliances are not suitable or capable of powering down devices after long periods of time from a triggering event.
Power-down circuits are well known in devices other than optical devices such as microscopes. For example, U.S. Pat. No. 5,595,672 (Sham et al.) discloses an automatic power interrupting apparatus for an electric appliance, such as a pressing iron. The apparatus of Sham et al. uses a touch sensitive switch (a capacitive device) to sense use of the device. When the human hand ceases contact with the switch, the apparatus activates an analog timing circuit (which uses capacitors as timing devices) to shut off power to the iron. The invention includes a second temperature sensitive shut-off circuit which powers down the device should the heating element in the iron reach a predetermined level. Although this patented device is arguably an improvement over earlier mercury switch shut-off devices for irons, the circuit in this invention uses a relatively expensive touch sensitive switch, and the analog timing circuit is incapable of timing long periods of time (e.g., anything longer than a minute or so).
Automatic control circuits for optical devices are also known in the art. U.S. Pat. No. 5,861,985 (Ikoh) discloses an automatic microscope including a detector for detecting the presence of an observer of the microscope within a predetermined range around the microscope. The detector of the patented invention also functions to power down the microscope when the observer leaves the predetermined range around the microscope. Although not described in detail in the patent, the detector in this invention appears to be a phototransistor. When ambient light incident on the transistor is blocked by a user, the phototransistor triggers appropriate circuitry to power up the illumination source. Similarly, when the observer leaves the predetermined range, the ambient light returns and the transistor switch sends an appropriate signal to power down the illumination source. The invention actually discloses three such phototransistor detectors. There are several disadvantages of this type of this circuit. First, the detectors are dependent on ambient light levels and the designers of this circuit presumably assume that the microscope will always be used in certain ambient light conditions, which may not always be the case. (For example, the circuit may not function properly in a low-ambient light environment.) Secondly, phototransistors are relatively expensive as compared to simple mechanical switches, and the patented invention uses three of them. Finally, and most importantly, the patent includes no teaching of a timing mechanism to control illumination. On the contrary, the illumination power source is tied directly to the detection of an observer. The sources turn on and off almost immediately upon detection of a person within range, or leaving range, respectively. The disadvantage of this control scheme is that it causes a cycling of the electronic drive circuitry and associated power sources, and it is well known in the art that repetitive cycling degradates life of certain light sources, such as incandescent light bulbs.
A similar control device for a microscope is disclosed in PCT International Application No. WO 98/18036 (Rühl et al.). The invention disclosed in this application includes a proximity sensor which senses the approach of an observer and controls illumination and motor function in the microscope in response thereto. This invention suffers from some of the same disadvantages described earlier.
Finally, a light source unit for an optical apparatus, namely an endoscope, is disclosed in European Patent Application No. 81105036.8 (Hattori). The apparatus of this invention includes a light emitting device and a light receiving device, both preferably arranged in the eyepiece of the endoscope. The light emitting device emits light-intensity modulated light. The received light is demodulated and filtered and a frequency component of the received signal is then compared to a Schmitt trigger reference voltage. When an observer places her eye proximate the eyepiece, more light from the emitter reaches the receiver. The signal level supplied to the Schmitt trigger then exceeds a predetermined value and associated electronics turns on a light source within the endoscope (or controls a shutter). Again, this invention teaches an “on-off” approach to controlling the light source. The source is either on or off; there is no teaching of a time delay in turning the source off.
Thus, it is seen that there is a longfelt need for a method and apparatus for automatically shutting off a microscope, and especially for a method and apparatus for digitally tracking elapsed-time within the microscope for the purpose of monitoring inactivity of a momentary SPST-switch after a period of time and turning off all sources of illumination within the microscope.